Perhaps the most common source of spectrally resolved or monochromatic light is a laser. Although single wavelength lasers have become quite common and inexpensive, widely tunable lasers are still very expensive. When a widely tunable source of light is required and lack of coherence is not an issue, incoherent light sources that utilize arc lamps or Tungsten Halogen lamps are frequently used. Their output is optically coupled into additional optical devices and spectrally resolved by narrow band filters or monochromators, which converts the output to a monochromatic spectrum. This approach results in complex and costly systems. FIGS. 1 and 2 show two prior art devices 100; 110 that use expensive coupling optics 13. The present invention, therefore, relates to an improved light source that has continuous wavelength tunability and that dispenses with the need for input slits or coupling optics.
Other devices are known to reduce an optical signal having several avelengths to several optical signals each having a particular wavelength. In telecommunications, optical multiplexer/demultiplexers are often used to either join several optical signals each having a separate wavelength into one signal or to separate an optical signal containing several wavelengths into several signals each having a different wavelength.
U.S. Pat. No. 4,999,489 to Huggins discloses a prior art slab Rowland spectrometer for multiplexing and demultiplexing optical telecommunication signals. This Rowland spectrometer uses an optical fibers for both inputs and outputs to either multiplex or demultiplex several frequencies within a light signal.
U.S. Pat. No. 4,387,955 to Ludman et al. also discloses a multiplexer/demultiplexer that uses a holographic reflective grating. The Ludman apparatus transmits either a coherent optical signal or an optical signal with a limited coherence over an input optical fiber. U.S. Pat. No. 4,707,056 to Biffner discloses a multiplexer/demultiplexer that uses a light conducting fiber and a slab waveguide for inputting a radiation source.
U.S. Pat. No. 5,550,375 to Peters et al. discloses an infrared-spectrometric sensor for detecting the presence of certain gases. The Peters et al. spectrometric sensor operates by using a concave mirror grating to separate the wavelengths from an infrared radiation source and measuring the absorption of the wavelengths in the gas to determine the presence of certain gases. The Peters et al. apparatus, however, uses an input slit.
None of the above multiplexer/demultiplexer or spectrometers, however, disclose an apparatus for creating a spectrally resolved light source that uses only an inexpensive, incoherent, spatially expansive, omnidirectional radiating source of light.
What is desired, therefore, is a light source that uses a relatively inexpensive, high power, and spatially expansive lamp, without expensive coupling optics to provide spectrally resolved output.